Transcript Dimensional Analysis - Day 1 Introduction to Chemistry and

Dimensional Analysis
Using units to solve problems
2.5 m X 1km
= 0.0025 km
1000 m
Conversion Factor – Used to change from
one unit to another.
Top equals the bottom
Conversion factors = 1
Example
How many seconds are in 3 hours?
s
(X)
min
hr
(3)
3hr X 60 min X 60 s = 10,800 s
1 hr
1 min
Procedure
1. Write down each unit in the problem once.
2. Draw lines to show conversion factors.
3. Use units to set up problems.
4. Put in numbers and solve.
Practice
Convert 10 cm to km
cm
m
km
Convert 10 cm to km
10 cm X
1m
100 cm
10 cm = 0.0001 km
X
1km =
1000 m
How many minutes are in 2.5 hours?
Conversion factor
2.5 hr x
60 min
1 hr
= 150 min
cancel
By using dimensional analysis / factor-label method,
the UNITS ensure that you have the conversion right
side up, and the UNITS are calculated as well as the
numbers!
Sample Problem
• You have $7.25 in your pocket in
quarters. How many quarters do you
have?
7.25 dollars
X
4 quarters
1 dollar
= 29 quarters
You Try This One!
If Jacob stands on
Spencer’s shoulders,
they are two and a half
yards high. How many
feet is that?
Learning Check
A rattlesnake is 2.44 m long. How
long is the snake in cm?
a) 2440 cm
b) 244 cm
c) 24.4 cm
Solution
A rattlesnake is 2.44 m long. How
long is the snake in cm?
b) 244 cm
2.44 m x 100 cm
1m
= 244 cm
Learning Check
How many seconds are in 1.4 days?
Unit plan: days
hr
1.4 days x 24 hr
1 day
x
min
??
seconds
How many gits
equal 5 hews?
•20 gits equal 1 erb
•1 futz equals 2 hews
•10 erbs equal 1 futz
How many drams is 4.0
grams?
• 1 pound = 7000 grains
• 16 ounces = 1 pound
• 3 scruples = 1 dram
• 454 grams = 1 pound
• 30 grams = 1 scruple
• A blacksmith has to put
new shoes on a stable of
20 horses. Each shoe
requires 3 nails. How
can he or she calculate
the number of nails that
must be brought to the
stable?